Evaluation of immunotherapeutic approaches for the potential treatment of infections caused by K1-positive Escherichia coli.

Levels of antibody to the K1 polysaccharide capsule were examined in sera from patients naturally infected with K1-positive Escherichia coli, in sera from volunteers vaccinated with a group B meningococcal vaccine, in immune globulin prepared for intravenous use, and in a preparation of murine IgM monoclonal antibody to group B meningococci. In a phagocytic assay, the monoclonal antibody in mouse ascites fluid killed K1-positive E. coli to a final dilution of 1:250,000 (48 ng of antibody protein/ml); no killing was observed with any of the other antibody sources. This monoclonal antibody, which required human complement and exhibited a prozone when high concentrations of antibody (greater than 6 micrograms/ml) were used, killed all K1-positive strains but none of the K1-negative strains of E. coli tested. Levels of K1-binding antibody in the sera of vaccinated volunteers exceeded antibody levels resulting from natural infection or present in commercially prepared immunoglobulin and were less than those obtained in mouse ascites fluid containing the monoclonal antibody.